What is the difference between a PCIe x16 slot and an express card

PCIex1 to PCIex16 Graphics Card Extension Board pcie x16 expansion slot 1 x PCI Express x16 slot, supporting PCIe and running at x16 * The PCIEX16 slot shares bandwidth with the M2C_CPU connector pcie slot width slot card, usb expansion card, pcie riser card, pcie graphics card, graphics card Time Stamp

pcie slot x16 Concept Product CP074-1 4 x NVMe SSD to PCIe x16 Mobile Rack for PCIe Expansion Slot with Blower Fan and Aluminum Heatsink